“Uniaxial hot pressing” and “hot isostatic pressing” of ceramics are well-known processing methods for sintering of advanced ceramics. These processes in the field of advanced ceramics might appear to be similar to the present invention, but are actually quite unrelated processes and are described in W. D. Kingery, “Introduction to Ceramics,” John Wiley & Sons, New York, 1960, pp. 72-74, 394, and also D. W. Richardson, “Modern Ceramic Engineering,” Marcel Dekker, Inc., New York, 1992, pp. 552-564, and also in the Background section of U.S. Pat. No. 6,159,400. A key distinction between hot pressing and the present invention is that hot pressing is conducted at approximately half the absolute melting temperature of the material, meaning it is in essence a solid-phase sintering process at high pressure, typically 6.9 to 34.5 MPa (1 to 5 ksi). Hot pressing also differs from the present invention in that pressure is applied to the material while it is still in a furnace. This requires that the pressing parts and molds be made from a highly heat-resistant material such as graphite. Graphite parts oxidize over time and are highly susceptible to wear, which makes the hot pressing process expensive and only in use for manufacture of high-cost specialized parts. Hot isostatic pressing diverges even further from the present invention, as described in Richardson, pp. 562-564.
The conventional method of forming ceramic tiles also differs from uniaxial hot pressing, hot isostatic pressing, and the present invention. The conventional method includes the steps of shaping and forming a ceramic composition containing ceramic powders, binder, and water, pressing the ceramic composition near room temperature and then firing the ceramic composition at high temperature near atmospheric pressure. The conventional ceramic tiles are rigid, brittle and cured to a permanently set (thermosetting) composition. Thus, the conventional ceramic tiles cannot be recycled by and reformed by heating and melting the ceramic tile like a thermoplastic polymer can be recycled and reformed. The ceramic tiles of this invention overcome the above deficiencies of conventional ceramic tiles.
U.S. Pat. No. 3,989,795 to Thomas McGee, entitled “Method of compressing ceramic refractory bodies,” describes “hot forging” of ceramic refractory blocks with low thermal conductivity for use in the bed of a steel-making furnace, and provides a method to reduce wear of the die or mold. McGee's method requires a complicated and expensive apparatus to remove the sides of the mold and avoid friction. Further, the preheated blank (or billet) in McGee's method must be smaller than the mold so that it can be placed inside. This requires the material flow out to engulf the entire space, which means that the material must have higher processing temperature in order to have low enough viscosity. The higher processing temperature is more expensive to operate, and tends to liquefy a greater portion of the starting material, resulting in a weaker final product.